1. Field of the Invention
The present invention relates to a closed caption control apparatus which is used by being built into or connected to a video playback apparatus, an audio playback apparatus, a video record-playback apparatus, or an audio record-playback apparatus, and which controls displaying of closed caption and other character information; and a method therefor.
2. Description of the Related Art
In playing-back video contents of television broadcasting or a DVD (Digital Versatile Disc) or the like, closed caption information for complementing audio information output along with video is provided. In a case of the television broadcasting, closed caption information is formed from teletex signals embedded in video signals, and transmitted by using identification signals (VBI signals) inserted into a vertical blanking interval. On a DVD or the like, multi-lingual closed caption information can be recorded along with video and audio. Further, in a case of digital high-vision broadcasting, closed caption information can be transmitted as sub video information.
It can be thought that the utilization of closed caption information is effective in a case where to hear the speech corresponding to an image is hard for not only a hearing impairment person or a defective hearing person, but also a person with normal hearing. For example, there are cases in which a background noise or music (BGM) mixed in a speech interferes hearing of the speech contents. Further, it goes without saying the case where a speed of speech to be heard is fast, and in a case where the speed of speech is extremely slow as well, it is hard even for the person with normal hearing to exactly listen the speech.
A technique in which a mode for displaying closed caption information corresponding to speech contents or the like is controlled in accordance with a difficulty in listening of the speech contents has been not realized yet in a conventional video playback apparatus or information display device.
On the other hand, several techniques of analyzing audio information have been known. For example, with regard to a determination on background noise, a method for estimating an SN ratio of input audio which is aimed for suppressing noise (for example, refer to Jpn. Pat. Appln. KOKAI Publication No. 7-306695) is well known. Further, with regard to a determination on musical sound, a method based on an autocorrelation coefficient of sound data (for example, refer to Jpn. Pat. Appln. KOKAI Publication No. 5-113797) is well known. Moreover, with regard to an estimation of a speed of speech, a method based on a dynamic features of a sound signal (for example, refer to Jpn. Pat. Appln. KOKAI Publication No. 5-289691) is well known.
An object of the present invention is to provide a closed caption control apparatus to display complementary closed caption information such that the contents of speech can be appropriately and exactly delivered to a viewer even in a situation in which it is hard to hear a speech in audio output, or control a mode for displaying the closed caption information, and a method therefor.